Package Substrate Build-Up Structure Without Groove Depth Variation
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Solution Overview
Problem
Conventional package substrates face issues with inconsistent groove depths and lateral etching of the first circuit layer during metal layer removal, leading to unreliable solder bonding and signal transmission, especially when miniaturization is required.
Innovation Solution
A package substrate with a heterogeneous layer made of a different material than the first circuit layer, allowing for controlled thickness and preventing lateral etching, ensuring consistent thickness and reliable solder bonding through a groove-free structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the metal layer is removed by etching to form grooves, then the board body can be separated from the circuit structure, but the first circuit layer is laterally etched causing damage or breakage
Solution Approach 1:
The patent segments the metal layer into two distinct layers: a first metal layer (copper) that is etched away for board separation, and a second metal layer (nickel or palladium) that remains to protect the first circuit layer. This segmentation allows differential etching behavior where the etchant selectively removes the first metal layer while leaving the second metal layer intact, thus preventing lateral etching of the first circuit layer.
Solution Approach 2:
The second metal layer acts as an intermediary protective barrier between the etchant and the first circuit layer. During the etching process, this intermediate layer prevents direct contact between the etchant and the first circuit layer, thereby eliminating lateral etching damage while still allowing the first metal layer to be removed for board separation.
2Ease of manufacture
If the first circuit layer is micro-etched during metal layer removal, then grooves are formed for solder ball embedding, but groove depth inconsistencies occur making bonding unreliable
Solution Approach 1:
The patent extracts the groove formation function from the etching process by completely removing the first metal layer while leaving the second metal layer intact. The grooves are formed by the absence of the first metal layer rather than by etching the first circuit layer, ensuring uniform groove depth determined by the thickness of the first metal layer rather than by variable etching depths.
Solution Approach 2:
The patent changes the material parameter of the metal layer from a single material to a heterogeneous two-layer structure with different etch resistances. This parameter change enables selective removal of the first metal layer while preserving the second metal layer, achieving consistent groove formation without lateral etching of the first circuit layer.
3Productivity
If the line width/line spacing of the first circuit layer is miniaturized, then high integration is achieved, but the first circuit layer is more likely to break due to lateral etching
Solution Approach 1:
The second metal layer serves multiple functions simultaneously: it acts as a protective barrier against lateral etching, provides structural support to miniaturized first circuit lines, and enables board separation when combined with the first metal layer. This multi-functionality allows the first circuit layer to be miniaturized without compromising its mechanical strength.
4Ease of manufacture
If the first circuit layer is laterally etched, then material is removed during metal layer removal, but signal transmission between first circuit layer and solder balls is damaged
Solution Approach 1:
The first metal layer is designed as a disposable sacrificial layer that is completely removed during the etching process. Its sole purpose is to facilitate board separation and groove formation, after which it serves no further function. The second metal layer, in contrast, is a permanent protective layer that remains to preserve the first circuit layer for signal transmission.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances solder ball bonding reliability and signal transmission, enabling mass production of miniaturized package substrates with improved yield and speed.
Implementation Method 1
removing the heterogeneous layer by etching to expose the first circuit layer
Implementation Method 2
copper is electroplated on the dielectric layer 12 and in the blind vias 120 to form a second circuit layer 13
Data Source
AI summary
Provided is a method for fabricating a package substrate including forming a heterogeneous layer on a board body; forming a first circuit layer on the heterogeneous layer; and forming a dielectric layer on the heterogeneous layer, such that the first circuit layer is embedded in the dielectric layer. After that, build-up circuit layers are provided, and the board body and the heterogeneous layer are removed, making the depth of the first circuit layer consistent to facilitate the bonding of a plurality of solder balls to the first circuit layer.